Three polarizers, centered on a common axis and with their planes parallel to each other, have transmission axes oriented at angles of 1, 2, and

Three polarizers, centered on a common axis and with their planes parallel to each other, have transmission axes oriented at angles of θ1, θ2, and θ3 from the vertical, as shown in Figure. Light of intensity Ii, polarized with its plane of polarization oriented vertically, is incident from the left onto the first polarizer. What is the ratio If/Ii of the final transmitted intensity to the incident intensity if
(a) θ1 = 45°, θ2 = 90°, and θ3 = 0°?
(b) θ1 = 0°, θ2 = 45°, and θ3 = 90°?